Zhen Wang

Fiber-reinforced polymer (FRP) laminates are prone to delamination because they lack continuous through-thickness reinforcement. Although multi-walled carbon nanotube (MWCNT) interlayers can improve interlaminar resistance, evidence has focused mainly on unidirectional carbon fiber-reinforced polymer (CFRP) and individual fracture modes. This study compared Mode I propagation and Mode II initiation toughness in CFRP, glass fiber-reinforced polymer (GFRP), and two carbon/glass hybrid laminates (HCRP and HGRP). Each system included unmodified (ORI), neat-epoxy interlayer (CON), and 0.1, 0.3, and 0.5 wt.% MWCNT conditions. The laminates were fabricated by N,N-dimethylformamide-assisted ultrasonication and hot pressing, and examined by ASTM D5528 double cantilever beam testing, ASTM D7905 end-notched flexure testing, and scanning electron microscopy. ORI and CON exhibited comparable toughness, indicating little contribution from the neat-epoxy interlayer alone. In all four systems, both toughness measures increased from 0.1 to 0.3 wt.% and decreased at 0.5 wt.%. At 0.3 wt.%, steady-state Mode I toughness increased by 31.2–51.2% and Mode II initiation toughness increased by 4.0–23.1% relative to CON. GFRP showed the highest absolute Mode I toughness, HCRP showed the largest Mode II improvement, and HGRP exhibited limited Mode II sensitivity. Matrix tearing, shear cusps, tortuous crack features, and distributed MWCNT pull-out at 0.3 wt.% contrasted with smoother regions, bundled or agglomerate-like structures, and cavities or pores at 0.5 wt.%. The effective MWCNT content therefore reflects a balance between nanotube-mediated energy dissipation and defect formation, modulated by fiber architecture and fracture mode.

Carbon fiber reinforced polypropylene (CF/PP) thermoplastics integrate the superior formability of fabrics with the recoverable characteristics of polypropylene, making them a pivotal solution for achieving lightweight designs in new energy vehicles. However, the prevailing methodologies for designing the structural performance of CF/PP vehicular components often omit the constraints imposed by the manufacturing process, thereby compromising product quality and reliability. This research presents a novel approach for developing a stamping–bending coupled finite element model (FEM) utilizing ABAQUS/Explicit. Initially, the hot stamping simulation is implemented, followed by the transmission of stamping information, including fiber yarn orientation and fiber yarn angle, to the follow-up step for updating the material properties of the cured specimen. Then, the structural performance analysis is conducted, accounting for the stamping effects. Furthermore, the parametric study reveals that the shape and length of the blank holding ring exerted minimal influence on the maximum fiber angle characteristic. However, it is noted that the energy absorption and crushing force efficiency metrics of the CF/PP specimens can be enhanced by increasing the length of the blank holding ring. Finally, a discrete optimization design is implemented to enhance the bending performance of the CF/PP specimen, accounting for the constraint of the maximum shear angle resulting from the stamping process. The optimized design resulted in a mass reduction of 14.3% and an improvement in specific energy absorption (SEA) by 17.5% compared to the baseline sample.

Understanding the thermo-stamping shear characteristics is not only essential to improve the forming quality of the glass fiber reinforced polypropylene (GFRPP) products but also critical to ensure their structure design reliability. Most previous studies primarily focused on the fiber yarn shear characteristics in the outer surface of the composite product, and omitted the shear angle variations of the inner layers, which might increase the failure risk to the product design. In this study, the U-shaped GFRPP rail was manufactured by the thermo-stamping process and scanned layer-by-layer through the X-ray micro-CT technology. Based on the scanning results, the differences in the shear angle variations of different layers at the same position, and within the same layer but different zones were analyzed, respectively. Finally, the effect of the temperature variation on the shear angle variation was analyzed by the simulation method. Results indicate that the interlaminar shear forces and slippages lead to the differences in shear angle variations among different layers. Intralaminar fiber yarn slippages and bending deformations caused the differences in shear angle variations within the same layer. The heat loss of the stamping molds resulted in a lower stamping temperature and further led to shear angle variation reduction. GRAPHICAL ABSTRACT